104 Maximum Depth of Binary Tree

原题链接：Maximum Depth of Binary Tree
非常简单的一道题，代码如下：

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param {TreeNode} root
    # @return {integer}
    def maxDepth(self, root):
        if root is None:
            return 0
        l = self.maxDepth(root.left) + 1
        r = self.maxDepth(root.right) + 1
        return l if l >= r else r